The characteristics of porphyrin, heme, bile pigment, and bile salt metabolism will be studied in two model systems. Factors regulating the formation of these metabolites will be studied in organ culture. The organ culture systems will be characterized by light and electron microscopy, by radioautography, and the capacity to synthesize macromolecules. Thereafter, the effect of inducers, metabolic poisons, and enzyme inhibitors on the synthesis of delta-aminolevulinic acid, hepatic bilirubin, bilirubin glucuronide, bile salt, and bile salt conjugates will be determined. In addition, fetal animal models will be used to characterize bile salt synthesis in the near-term fetus. For this purpose, fetal dogs and monkeys will be prepared in utero with vascular, bile duct, and intestinal catheters and the following will be measured: bile salt synthesis, placental transfer of bile salt, and intestinal bile salt absorption.